Linux Basic Learning-day nineth (Shell Basics)

2016-08-10

Content of the lesson:

Shell Script Basics:

Variable

Operation

Bash Test (digital test, character test, file test, combination test)

Read command

Variable action:

1. Data storage format

2, the operation of the participation

3, the data range indicated

Variable type:

1. Local Variables

2. Environment (Global) variables

3. Special variables

Hump named variable: one letter capitalized per word

local variable : The active scope is the current shell process and is not valid for Shell processes other than the current shell, including the current Shell's child shell process

Configuration file: ~./BASHRC ~/.bash_profile

Variable assignment: Varname=value

Set: Show variables that have been set

unset VARNAME: Releasing variables (it is best to get into the habit of releasing variables in time)

Environment (GLOBAL) variables:

Configuration files:/etc/profile,/etc/profile_d/*.sh

Variable assignment: ①export varname=value

②varname=value

Export VARNAME

Env/printenv/export: Display Environment variables

[[email protected] shells]# envxdg_session_id=57hostname=centos7.2selinux_role_requested=term= xtermshell=/bin/bashhistsize=5000ssh_client=10.1.24.55 56521 22selinux_use_current_range=ssh_tty=/ Dev/pts/0user=rootls_colors=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or =40;31;01:mi=01;05;37;41:su=37;41:sg=30;43:ca=30;41:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01; 31:*.arc=01;31:*.arj=01;31:*.taz=01;31:*.lha=01;31:*.lz4=01;31:*.lzh=01;31:*.lzma=01;31:*.tlz=01;31:*.txz=01; 31:*.tzo=01;31:*.t7z=01;31:*.zip=01;31:*.z=01;31:*. Z=01;31:*.dz=01;31:*.gz=01;31:*.lrz=01;31:*.lz=01;31:*.lzo=01;31:*.xz=01;31:*.bz2=01;31:*.bz=01;31:*.tbz=01;31 :*. tbz2=01;31:*.tz=01;31:*.deb=01;31:*.rpm=01;31:*.jar=01;31:*.war=01;31:*.ear=01;31:*.sar=01;31:*.rar=01;31:* . alz=01;31:*.ace=01;31:*.zoo=01;31:*.cpio=01;31:*.7z=01;31:*.rz=01;31:*.cab=01;31:*.jpg=01;35:*.jpeg=01;35:*. Gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35:*.xbm=01;35:*.xpm=01;35:*.tif=01;35:*.tiff=01;35:*.png=01;35:*.svg=01;35:*.svgz=01;35:*.mng=01;35:*.pcx=01;35:*.mov =01;35:*.mpg=01;35:*.mpeg=01;35:*.m2v=01;35:*.mkv=01;35:*.webm=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*. mp4v=01;35:*.vob=01;35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35:*.flc=01;35:*. avi=01;35:*.fli=01;35:*.flv=01;35:*.gl=01;35:*.dl=01;35:*.xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.cgm=01;35:*.emf= 01;35:*.axv=01;35:*.anx=01;35:*.ogv=01;35:*.ogx=01;35:*.aac=01;36:*.au=01;36:*.flac=01;36:*.mid=01;36:*.midi= 01;36:*.mka=01;36:*.mp3=01;36:*.mpc=01;36:*.ogg=01;36:*.ra=01;36:*.wav=01;36:*.axa=01;36:*.oga=01;36:*.spx=01; 36:*.xspf=01;36:mail=/var/spool/mail/rootpath=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/binpwd=/ Root/shellslang=en_us. utf-8selinux_level_requested=histcontrol=ignoredupsshlvl=1home=/rootlogname=rootssh_connection=10.1.24.55  56521 10.1.252.77 22lessopen=| | /usr/bin/lesspipe.sh %sxdg_runtime_dir=/run/user/0_=/usr/Bin/envoldpwd=/root 

unset VARNAME: Releasing variables

Special Variables :

Positional variables:

$1,$2...${10}: Represents the 1th, 2..10 position variable

$#: Number of variables

Other variables

$0:shell file name (including path)

Baseename $: Only the base name (file name, excluding path) is displayed

DirName $: Show only the path, not the name

[Email protected] shells]# basename/etc/passwdpasswd[[email protected] shells]# dirname/etc/passwd/etc

$*: passed to all parameters of the script (as a parameter output)

[Email protected]: All parameters passed to the script (the number of parameters of the original number of parameters output)

$?: The status return value of the previous command, 0 indicates that the previous command executed successfully, and the other indicates that the command was executed incorrectly

Operation:

+-*/:

%: Take the remainder

* *: Second party, 2**3 equals 2 of three times

+=:a+=2 = = A=a+2

-=:a-=2 = = A=a-2

*=:a*=2 = = A=a*2

/=:a/=2 = = A=A/2

%=:a%=2 = = a=a%2

The difference between ++a and a++

A++:a=a,a=a+1

++a:a=a+1,a=a

To implement arithmetic operations:

(1) Let var= arithmetic expression

(2) var=$[arithmetic expression]

(3) var=$ ((arithmetic expression)) ""

(4) var=$ (expr arg1 arg2 arg3 ...) "Note that each parameter must have a space"

(5) Declare–i var= value

(6) echo ' Arithmetic expression ' | Bc

Conditional test Expression

[  ]

[[  ]]

Test expression

Bash test Type: Digital test, character test, file test, combined condition test

Digital test:

-eq: Equals

-ge: greater than or equal to

-GT: Greater Than

-le: Less than or equal to

-LT: Less than

-ne: Not equal to

Character testing (typically using double brackets [[]]):

= =:

!=:

=~:

-Z ' string ' string is empty, empty is true, not empty for false

-N ' string ' string is not empty, not empty is true, empty is false

File test:

Existence of:

-E:

File type: the

-D: Whether it is a directory

-F: is normal file

-B: Whether it is a block device file

-C: Whether it is a character device file

-H: Equivalent to-l, whether it is a linked file

-P: Whether it is a pipe file

-S: is a socket file

File permissions:

-r: Whether Read permission is available

-W: Write permission

-X: Whether there are execute permissions

-U: Do you have SUID permissions

-G: Do you have Sgid permissions

-K: Do you have sticky permissions

File size test:

-S FILE: exists and is not empty;

Whether the file is open:

-T FD:FD indicates whether the file descriptor is open and related to a terminal

-N File: whether the files have been modified since the last time they were read

-O File: Whether the current active user is a file owner

-G file: whether the current active user is a group of files

Combination condition test:

Expression1-a EXPRESSION2 and

Expression1-o EXPRESSION2 or

Read command

Use read to assign the input value to one or more shell variables:

-p Specifies the prompt to display

Read-p "Enter a filename:" FILE

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Linux Basic Learning-day nineth (Shell Basics)